@HenrikEkman eipä kestä

Some operators show the frequencies on their websites, some don't. I've had to do quite a bit of studying as well since buying the X50-5G, since I wasn't very familiar with LTE and 5G networks before. I'll give some links but this forum says external links are illegal, so I'll give you some google keywords instead.

DNA is is quite open about it and posts them on the website, they usually use either 3500MHz band for high speed where there's more people or 700MHz band to get better reception indoors. The frequency bands reserved for operators in Finland can be found by googling "Matkaviestinverkkojen taajuudet", all operators have a 700MHz band reserved for 5G, but not sure how they use them. Based on cellmapper dot net it would seem that they all use the 700MHz N28 band to get basic 5G coverage.

What puzzled me for a long time was that my Deco doesn't report any 5G bands in the "Internet" section, but if I get to the "Additional Information" section I see things like: LTE BAND 3, LTE BAND 8, LTE BAND 1, NR5G BAND 28. I've come to the conclusion that the UI must be wrong and the additional information is actually showing the bands it is using, maybe it doesn't show the 5G band because there's only a single band, don't know... Either way, you can map these band numbers to frequencies by for example googling "5G NR frequency bands", the Wikipedia page works for me. As far as I know LTE and 5G use the same band numbers, but 5G just has more bands available. 28 and 48 are common 5G bands in Finland while 1, 3, 8 and 20 are common LTE bands.

NSA in this context means non-standalone mode (not the National Security Agency ;) which means the base communication with the network goes over LTE, but the 5G network is used for faster download and upload speeds for data. Therefore, in 5G NSA mode you must have access to both 4G and 5G bands for the network to work. I'm not sure if it's the ISP configuration or the X50-5G, but I haven't been able to get it to standalone mode. It probably wouldn't make sense anyway, since the 700MHz frequency will probably be slower than 4G, especially for single band upload, unless combined with at least one 4G band (of which the router seems to strongly prefer 1800MHz for me). And based on my experimentation the router is sometimes giving me double the upload speed in 5G mode compared to the 4G mode, so I'm inclined to believe it does use the 5G network properly. There's not a big difference in the download speed for me, 5G is only slightly higher, but DL often goes to around 200Mbps which is plenty in the middle of a forest.

You are correct, my recent observations are based on v1.2.0 and I'm not using any frequency locking or band locking. I've only been on v1.2.0 for a couple of days but so far I've seen less weird activity than before. It's worth to note that some people have had high CPU usage for that firmware though, especially if using QoS and multiple Decos, and it's not possible to downgrade it to 1.1.x after upgrading. But it's worked for me so far, and gives me a VPN connection to the router which is nice especially if it disappears from the cloud service but is otherwise working (which has happened).